Conventionally, an art is known reducing PM (Particulate matter) included in exhaust gas of a diesel engine with a particulate removing filter referred to as a DPF (Diesel Particulate Filter).
When the temperature of the exhaust gas is higher than the regeneration temperature of the DPF, the PM collected in the DPF can be made harmless and removed. On the other hand, when the temperature of the exhaust gas is lower than the regeneration temperature of the DPF, the PM collected in the DPF cannot be made harmless and removed. Then, in this case, as regeneration control of the DPF, the temperature of the exhaust gas must be made higher than the regeneration temperature regularly by using EGR and exhaust gas with excessive fuel so as to make the PM collected in the DPF harmless and remove it.
The Japanese Patent Laid Open Gazette 2004-183506 discloses construction in which, in the case of manual regeneration control of a DPF for exhaust gas, engine speed is increased to a predetermined value so as to make the temperature of the exhaust gas is higher than the regeneration temperature of the DPF. The manual regeneration control is regeneration control performed based on certain manual operation by an operator.
However, in the construction disclosed by the Japanese Patent Laid Open Gazette 2004-183506, in the case of the manual regeneration control of the DPF, the engine speed is always increased to the predetermined value. Therefore, when the temperature of the exhaust gas is close to the regeneration temperature of the DPF in the operation till then, the engine speed is increased excessively and fuel is consumed uselessly.